implement simulation shell

src/lib/sim/Simulation.h

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <random>
+#include <vector>
+
+#include "EntityId.h"
+#include "FireEvent.h"
+#include "BlueprintDropEvent.h"
+#include "GameConfig.h"
+#include "Tick.h"
+
+class Simulation
+{
+public:
+    explicit Simulation(const GameConfig& config, unsigned int seed = 0);
+
+    // Advances the simulation by one tick. Tick order per architecture.md §Tick Order.
+    // Currently a stub; subsystems are plugged in across Steps 3-7.
+    void tick();
+
+    // Returns all fire events accumulated since the last drain, clearing the
+    // internal queue. Call once per rendered frame (REQ-SHP-FIRING-BEAM).
+    std::vector<FireEvent> drainFireEvents();
+
+    // Returns all blueprint drop events since the last drain.
+    std::vector<BlueprintDropEvent> drainBlueprintDropEvents();
+
+    Tick currentTick() const;
+
+private:
+    EntityId allocateId();  // Strictly increasing; never returns kInvalidEntityId.
+
+    const GameConfig& m_config;
+    std::mt19937 m_rng;
+
+    Tick m_currentTick;
+    EntityId m_nextId;  // starts at 1; 0 is kInvalidEntityId.
+
+    std::vector<FireEvent> m_fireEvents;
+    std::vector<BlueprintDropEvent> m_blueprintDropEvents;
+};